An element has the electron configuration 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10. Which of the following statements about this element is correct?
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Correct answer
A. It is a d-block element and its highest occupied principal energy level is 7.
Principle or equation
The periodic table block is determined by the subshell being filled last according to the Aufbau principle. The highest principal quantum number n with electrons is the period. The configuration ends with 6d10, so the last electron enters a d subshell, making it a d-block element. The highest occupied principal energy level is 7 (from 7s2).
Why this answer is correct
The configuration shows that after filling 7s2, the 5f and 6d subshells are filled. The last subshell filled is 6d, which is a d subshell, so the element is in the d-block. The highest principal quantum number with electrons is 7 (7s2), so the element is in period 7. Thus option A is correct.
Example
For an element ending in 6d10, its block is d and period is 7.
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